In an existing Vehicle-to-X (V2X) communications system, nodes can exchange information with each other in a distributed manner to obtain information about occupancies of radio resources by the nodes, a topology between the nodes, and other information.
In an existing algorithm, e.g., the Mobile Slotted ALOHA (MS-ALOHA) algorithm, only received Frame Information (FI) is buffered in respective slots of each frame, and the received respective FI in a frame is processed collectively in a transmission slot. Even if there is collision occurring between slot resources before the transmission slot, the collision will not be detected until the instance of time of the transmission slot arrives, and may be detected on a late occasion. There may be a stressing burst peak processing load on the transmission slot.
In another existing algorithm, e.g., the State Update ALOHA (SU-ALOHA) algorithm, whether FI is received is determined in each slot of each frame. If FI is received, the slot state table will be updated, so that collision occurring between transmission slots can be detected timely to reselect an available transmission slot, and also smooth the stressing peak processing load on the transmission slot in the MS-ALOHA algorithm. However since the one-dimension slot state table is reset periodically, the one-dimension slot state table can not be processed according to integral Frame Information (FI) received in a frame, a multi-table processing result of the one-dimension slot state table can only be obtained with the effect of approaching the MS-ALOHA algorithm provided with the integral FI information, and it may not be necessary to process the slot state table in each slot if there is no collision occurring between slot resources.
A particular description will be given below:
The MS-ALOHA algorithm will be described taking a maintenance process as an example:
If FI is received in a slot n (0<=n<=N−1), then N information fields in the FI is filled into a row corresponding to the slot n in FIG. 1 (there are four status values of each information field, including an idle state, an occupied state, a collision state, and a two-hop occupied state, which are simply represented respectively as XX in FIG. 1); and if there is not any information received by a node in the slot n, then N columns of default states are filled into the row corresponding to the slot n in FIG. 1.
Here there are five possible states of any element, including the four states and the default state as mentioned above.
If a transmission slot is selected as a slot p, then respective slots are detected, and the old slot information in FIG. 1 is overwritten with new slot information (that is, information in latest N slots is kept in the window all the time), until the slot p arrives. If the slot p arrives, then for the (N−1) elements in the column corresponding to the slot p, it is determined using the N*N slot state buffer table whether there is such one or more occupied states (10) in the (N−1) elements that a Source Temporary Identifier (STI) thereof is different from the STI of the slot, and if so, then it is determined whether the priority of the slot is the highest, and if not, then a failure of occupying the slot is determined, and an idle slot needs to be reselected immediately as a transmission slot. Apparently the collision occurring between the slot resources will not be determined according to the information fields in the previously received FI until the slot p arrives, so the collision occurring between the slot resources may be determined on a late occasion.
The information in the N*N slot state buffer table needs to be monitored for the slot p, and the slot states in the column corresponding to the transmission slot p, in the (N−1)*N slot state buffer table need to be converted except for the corresponding row, where in the worst case, if every two information fields in each slot need to be compared with each other to obtain a final state conversion result, then the temporal complexity of processing the N slots will be O(n3), thus resulting in a pressing burst peak processing load on the transmission slot.
The SU-ALOHA algorithm will be described taking requesting for a new slot as an example:
A node occupies two slots and maintains two one-dimension state tables as illustrated in FIG. 2.
If the slot 7 is the expected new slot requested for in the slot 3, then since the one-dimension slot state table corresponding to the slot 2 has just been reset periodically in the slot 2, the information in the slot state table only includes information of transmission slot 2. The one-dimension slot state table corresponding to the slot 6 is reset periodically in the slot 6 in the last frame so that information of the slot 3, the slot 4 and the slot 5, received in the slot 3 is not integral. The information in the one-dimension slot state table corresponding to the slot 3, generated from the one-dimension slot state table corresponding to the slot 6 is not integral either.
In the processing of buffering the slot states in the one-dimension slot state table in each slot, since the compared information fields in the FI correspond to the slot state units in the one-dimension slot state table per slot, the temporal complexity of processing the N slots is O(n), thus smoothing the stressing peak processing load on the transmission slot in the MS-ALOHA algorithm.
In summary the prior art suffers from the following technical problems:
In the MS-ALOHA algorithm, respective FI received in a frame is processed collectively only in a transmission slot in the frame to update a slot state table, thus resulting in a stressing peak processing load on the transmission slot, where the temporal complexity of processing is O(n3); and in the SU-ALOHA algorithm, it may not be necessary to update the slot state table in each slot if there is no collision occurring between slot resources because the temporal complexity of processing would have become higher if the slot state table were updated in each slot. Apparently there may be low temporal flexibility in updating the slot states in the prior art.